1. Field of the Invention
The invention relates generally to the field of materials. More particularly, the invention relates to a composition, apparatus and/or photovoltaic device that includes a collection layer. The collection layer can include undesirable materials such as excess precursor(s), secondary phase precipitates, impurities, residue and/or debris and its function can be to sequester these undesirable materials in a safe location away from sensitive device locations such as semiconductor junction regions. The invention thus relates to compositions, apparatus and/or devices that can be characterized by the presence of a collection layer.
2. Discussion of the Related Art
A plethora of methods have been used for the synthesis of films (coatings) composed of materials from the CIS (copper indium selenide) material system and related alloys, but each of the previous methods has characteristics that limit their applicability to the economical manufacture of films with properties suitable for application to optoelectronic devices, such as photovoltaic (PV) devices. PV devices require an optical absorber that also provides sufficiently long minority carrier lifetimes to enable the collection of the minority carriers by the electrodes in the device""s structure without excessive recombination. In all semiconductor materials minority carrier lifetimes are dependent on the defect structure of those materials. The control of defect structure is critical to the successful manufacture of PV devices. Similarly the defect structure of high-temperature superconductors, electroluminescent phosphors, and other (opto-)electronic materials control the physical properties that determine their efficacy for their respective intended uses.
Thin film optical absorbers are more economical than thick film absorbers or coatings because they require a smaller amount of the precursor materials than thick films or coatings. The formation of thin films with desirable defect properties is predominately determined by the method by which they are synthesized. Early efforts to fabricate thin film CIS PV devices that relied on the steady-state co-deposition of the constituent elements copper, indium, and selenide were not very successful1. The first efficient thin film CIS PV devices were achieved by a two-step process that relied on the sequential deposition of two layers onto a substrate at high temperature, each with different composition. These layers reacted and intermixed to yield a nominally uniform composition throughout their combined thickness, and resulted in films with desirable defect structures2-4. Variations of this method have been demonstrated, based on different temperatures, numbers of layers, and compositions thereof.5,6. Other fundamentally different approaches have been described that rely on, for example: (1) heating stacked layers of the metals (e.g., copper, indium and gallium) and selenide that have been sequentially deposited at low temperatures7-9, (2) thermal reaction of metallic layer precursors in hydrogen selenide10,11 or selenide vapor12, (3) thermal reaction of oxide particulate precursor mixture layers at high temperatures13, and (4) thermal reaction of binary (Cu,Se) and (In,Se) precursor layers14,15.
An economical process for the manufacture of thin films of these sorts of non-stoichiometric multinary compounds needs to both efficiently use raw materials and be rapid (for low cost), but must be flexible to enable control of the defect structures required for high performance. None of the methods in the prior art provide an optimal combination of these features. Heretofore, the requirements of efficient raw material utilization, rapid fabrication, and flexibility for optimization of defect properties referred to above have not been fully met. What is needed is a solution that simultaneously addresses all of these requirements.
There is a need for the following embodiments. Of course, the invention is not limited to these embodiments.
According to an aspect of the invention, a method comprises: exerting a pressure between a first precursor layer that is coupled to a first substrate and a second precursor layer that is coupled to a second substrate; forming a composition layer; and moving the first substrate relative to the second substrate, wherein the composition layer remains coupled to the second substrate. According to another aspect of the invention, a method comprises: applying an electrostatic field across a first precursor layer that is coupled to a first substrate and a second precursor layer that is coupled to a second substrate; forming a composition layer; and moving the first substrate relative to the second substrate, wherein the composition layer remains coupled to the second substrate. According to another aspect of the invention, a method comprises: locating a template within at least one of a first precursor layer that is coupled to a first substrate and a second precursor layer that is coupled to a second substrate; forming a composition layer; and moving the first substrate relative to the second substrate, wherein the composition layer remains coupled to the second substrate. According to another aspect of the invention, a method comprises: providing a surfactant as an impurity within at least one of a first precursor layer that is coupled to a first substrate and a second precursor layer that is coupled to a second substrate; forming a composition layer; and moving the first substrate relative to the second substrate, wherein the composition layer remains coupled to the second substrate. According to another aspect of the invention, an apparatus comprises: a first holder; a second holder coupled to the first holder; a linkage coupled to the first holder and the second holder to move the first holder relative to the second holder; a reusable tool coupled to the first holder, the reusable tool including a raised patterned surface; and a release layer coupled to the raised patterned surface of the reusable tool. According to another aspect of the invention, a composition comprises: a composition layer defining a first surface and a second surface, the composition layer including a collection layer that is located closer to the first surface than to the second surface.
These, and other, embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such substitutions, modifications, additions and/or rearrangements.